U.S. patent application number 15/302181 was filed with the patent office on 2017-01-26 for process for forming a component by means of additive manufacturing, and powder dispensing device for carrying out such a process.
The applicant listed for this patent is GE AVIO S.R.L.. Invention is credited to Mauro VARETTI.
Application Number | 20170021456 15/302181 |
Document ID | / |
Family ID | 50943488 |
Filed Date | 2017-01-26 |
United States Patent
Application |
20170021456 |
Kind Code |
A1 |
VARETTI; Mauro |
January 26, 2017 |
PROCESS FOR FORMING A COMPONENT BY MEANS OF ADDITIVE MANUFACTURING,
AND POWDER DISPENSING DEVICE FOR CARRYING OUT SUCH A PROCESS
Abstract
A component is formed by means of additive manufacturing by
repeating a series of cycles, where each cycle has a depositing
step for forming a powder layer of substantially constant
thickness; a pre-heating step, for pre-heating the powder layer;
and a melting step, for melting some areas of said powder layer by
means of an energy beam so as to form a horizontal section of the
component that must be obtained; at the end of all cycles, the top
surface of the horizontal section that has been formed is lowered
until it reaches a predetermined height; the pre-heating step is
performed by moving a heat source above the powder layer at the
same time as the depositing step, at least for an initial part of
the pre-heating step.
Inventors: |
VARETTI; Mauro; (Collegno,
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GE AVIO S.R.L. |
Rivalta Di Torino |
|
IT |
|
|
Family ID: |
50943488 |
Appl. No.: |
15/302181 |
Filed: |
April 10, 2015 |
PCT Filed: |
April 10, 2015 |
PCT NO: |
PCT/IB2015/052625 |
371 Date: |
October 6, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2035/0811 20130101;
B23K 15/0026 20130101; Y02P 10/295 20151101; B23K 26/0869 20130101;
B29C 64/205 20170801; B23K 26/342 20151001; B33Y 30/00 20141201;
B33Y 40/00 20141201; B23K 26/60 20151001; B22F 3/1055 20130101;
B23K 26/702 20151001; B23K 15/0086 20130101; B22F 2003/1056
20130101; H05B 6/44 20130101; B33Y 10/00 20141201; B29C 35/0805
20130101; Y02P 10/25 20151101; B29C 64/153 20170801; B23K 15/002
20130101; H05B 6/101 20130101; B29C 2035/0855 20130101 |
International
Class: |
B23K 26/342 20060101
B23K026/342; H05B 6/44 20060101 H05B006/44; B33Y 10/00 20060101
B33Y010/00; B23K 26/70 20060101 B23K026/70; B33Y 40/00 20060101
B33Y040/00; B23K 15/00 20060101 B23K015/00; B23K 26/08 20060101
B23K026/08; B23K 26/60 20060101 B23K026/60; H05B 6/10 20060101
H05B006/10; B33Y 30/00 20060101 B33Y030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2014 |
IT |
TO2014A000309 |
Claims
1. A process for forming a component by additive manufacturing, the
process comprising the steps of: a) depositing powders having the
same composition as said component so as to define a powder layer
having a substantially constant thickness; b) pre-heating said
powder layer; c) carrying out a melting of some areas of said
powder layer by an energy beam so as to form a horizontal section
of said component; d) lowering the top surface of the horizontal
section formed until it reaches a predetermined height; e)
repeating the previous steps until all horizontal sections of said
component are formed; wherein the pre-heating step is carried out
by moving a heat source above said powder layer at the same time as
the depositing step, at least for an initial part of the
pre-heating step.
2. The process according to claim 1, wherein the pre-heating step
is carried out by induction.
3. The process according to claim 1, wherein the melting step is
carried out by moving said energy beam on said powder layer
simultaneously to the depositing and pre-heating steps, at least
for an initial part of the melting step.
4. The process according to claim 1, wherein the depositing and
pre-heating steps are carried out by moving a single powder
dispensing device along an advancement direction.
5. The process according to claim 1, wherein the pre-heating power
is varied between various areas of the powder layer that are
pre-heated.
6. The powder dispensing device movable along an advancement
direction and comprising at least one of: a powder dispenser for
dropping a layer of powder from the powder dispensing device; a
leveling element adapted to pass on powder dropped during the
advancement of the powder dispensing device for making the
thickness of said powder layer even; wherein the powder dispensing
device further comprises at least one heat source for pre-heating
said powder layer.
7. The powder dispensing device according to claim 6, wherein said
heat source and the powder dispensing device and/or leveling
element are elongated along directions that are parallel to each
other and orthogonal to the advancement direction.
8. The powder dispensing device according to claim 6, wherein said
heat source comprises a plurality of induction coils having
respective vertical axes.
9. The powder dispensing device according to claim 7, wherein said
heat source comprises a first and a second row of induction coils
with each having a respective vertical axis, each induction coil of
said first row being associated with, and adjacent to, a
corresponding induction coil of said second row so as to close the
magnetic field lines.
10. The powder dispensing device according to claim 6, wherein the
powder dispensing device further comprises a shield arranged around
said induction coils, except for a bottom side which faces, in use,
said powder layer.
11. The powder dispensing device according to claim 6, wherein the
powder dispensing device further comprises an adjustment device for
varying the pre-heating power between various areas of said powder
layer that are pre-heated.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Disclosure
[0002] The present invention relates to a process for forming a
component by means of additive manufacturing.
[0003] 2. Description of the Related Art
[0004] As is known, additive manufacturing techniques consist in
repeating cycles during which successive horizontal sections of the
component to be formed are created. In particular, a powder layer
is deposited at the beginning of each cycle, where such a layer has
a substantially constant thickness, and the powders have the same
composition as the component that must be formed; then specific
areas of the powder layer are melted by scanning a focused energy
beam, generally a laser beam or an electron beam, where such areas
are selected according to a mathematical model, which represents
the geometry and the size of the component that must be formed. In
other words, in the areas where the powders are melted, a
continuous structure is formed which defines a corresponding
horizontal section of the component.
[0005] Once the melting is complete, the part of the component that
was already formed is lowered by a quantity equal to the thickness
of the powder layer which is deposited each time, so as to move to
the next cycle. Finally, once all cycles are completed, the
residual powders are removed.
[0006] For materials with high contraction coefficients during
their solidification, the melting step must be preceded by a
pre-heating step of the powder layer (to increase the temperature
thereof to a level which is in any case lower than the melting
temperature), in order to reduce the thermal shock and therefore
avoid the formation of residual tensions and imperfections in the
component being formed.
[0007] Normally, the pre-heating step is carried out by means of a
defocused electron beam but this solution is poorly
satisfactory.
[0008] On the one hand, the operating times are relatively long,
especially for relatively large components, because the pre-heating
step is carried out after the powder layer has been completely
deposited. Secondly, the electron beam is not suitable for being
used for all materials, because it must operate under partial
vacuum where the residual gas is very low pressure helium gas.
Indeed, these ambient conditions are not suitable for those
materials (for example aluminium alloys) which suffer from
evaporation in the case of vacuum ambient.
[0009] To obviate this last disadvantage, other techniques are
generally used for the pre-heating step. For example, International
Patent Application WO2013152750A1 describes a system provided with
an induction coil, which is embedded in an insulator material
surrounding a cylindrical cavity housing the component being
formed. Nevertheless, a system of this type is relatively
cumbersome and does not allow the pre-heating temperature to be
varied between the various areas of the powder layer.
SUMMARY OF THE DISCLOSURE
[0010] It is the object of the present invention to provide a
process for forming a component by means of additive manufacturing,
which allows the above-described problems to be resolved in a
simple and cost-effective manner.
[0011] According to the present invention, a process is provided
for forming a component by means of additive manufacturing, as
defined in claim 1.
[0012] The present invention further relates to a powder dispensing
device for carrying out a process of additive manufacturing, as
defined in claim 6.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a better understanding of the present invention, a
preferred embodiment thereof is now described, by way of a mere
non-limiting example, with reference to the accompanying drawings,
in which:
[0014] FIGS. 1 to 4 are diagrams showing some steps of a preferred
embodiment of the process for forming a component by means of
additive manufacturing according to the present invention;
[0015] FIG. 5 is a simplified cross section of a powder dispensing
device, diagrammatically shown in FIGS. 1 to 4; and
[0016] FIG. 6 is a bottom view, of a back portion of the powder
dispensing device in FIG. 5.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0017] Numeral 1 in FIGS. 1 to 4 indicates a component that is
formed starting from metallic powders, by means of an additive
manufacturing technique, that is a "layer by layer" type of
manufacturing technique.
[0018] These layer by layer manufacturing techniques are referenced
to in literature by different acronyms, for example acronyms such
as "Direct Laser Forming" (DLF), "Direct Metal Laser Sintering"
(DMLS), "Selective Laser Melting" (SLM) or "Electron Beam Melting"
(EBM).
[0019] The composition of the metallic powders is close to the one
of component 1 that must be formed. In particular, titanium alloys
are commonly used in the aeronautics field, for example a known
alloy with the abbreviation Ti6-4 or Ti6AI-4V (having 6% aluminium
and 4% vanadium). With regard to titanium alloys, the 4% vanadium).
With regard to titanium alloys, the temperatures required to obtain
the melting of the powders may reach 1800.degree. C., according to
the particular alloy used.
[0020] The process is carried out by means of a machine 11
(diagrammatically and partly shown) comprising a work chamber 12,
which houses a base plate 13, also called "starting platform", on
which the first powder layer is deposited.
[0021] The base plate 13 is actuated (in a manner not shown) to
translate progressively downwards along the vertical direction
(arrow V), in response to a control unit 16 commands. Obviously the
base plate 13 must be made of a material which is capable of
resisting the high temperatures for melting the powders.
[0022] The metallic powders are deposited by a distributor device
14, which will be described in greater detail below, so as to form
overlapping successive layers 22.
[0023] Machine 11 also comprises an emitter or gun 15 for emitting
an energy beam downwards, for example a focused electron beam or a
focused laser light beam, so as to obtain the melting or the
sintering of the powders: emitter 15 is actuated and controlled by
the control unit 16 so as to melt each powder layer locally, at the
areas to be actually formed.
[0024] The laser is generally used for powder layers 22 having
thickness up to 40 .mu.m, while the electron beam for a thickness
up to 180 .mu.m.
[0025] Emitter 15 and the base plate 13 are preferably movable with
respect to one another to carry out the scanning of the top surface
of each powder layer 22 by means of the energy beam. Alternatively
to or in combination with this relative movement, a system of
driven deflectors for deflecting the energy beam towards the
desired areas may be provided.
[0026] Furthermore, machine 11 may comprise a system (not shown)
for generating the vacuum in chamber 12, and/or a system (not
shown) for emitting an inert gas jet (for example argon and helium)
into chamber 12 towards the melting area, for example to protect
the material that is being melted from oxidization.
[0027] The selection of the areas to be melted is based on a
three-dimensional mathematical model generated beforehand and
corresponding to the shape and to the size desired for component 1.
For example, the three-dimensional model may be generated by means
of computer assisted design (CAD) and transferred to the control
unit 16 in the form of "files". The three-dimensional model is
stored in the control unit 16 and is divided into overlapping
horizontal levels, each associated to a relative horizontal section
of component 1, which is formed by locally melting corresponding
areas of the powder layer 22.
[0028] FIG. 1 depicts an intermediate step of the formation of
component 1. In this step, it is assumed that a lower portion 17
and a series of pedestals 18 have already been formed. The
pedestals 18 are also defined in the three-dimensional model
together with component 1, are formed in chamber 12 to keep
component fixed to plate 13 during forming and, at the same time,
to space portion 17 apart from plate 13. The pedestals 18 are
removed at the end of the manufacturing process.
[0029] A top portion 19 still to be formed is indicated in FIGS. 1
to 4 with a dotted line. The portions 17, 18, already formed, are
surrounded by a mass of residual powders 20, which were deposited
in layers beforehand but which were not subjected to melting.
[0030] Preferably, the powders have a grain size included in the
range from 20 to 150 .mu.m. The choice of the powder grain size is
a compromise between various needs: having increased manufacturing
speed (which would favor powders with larger grain size); having
good shape and homogeneity accuracy in the structure of component 1
which must be formed; being able to easily empty any cavities
and/or pores of component 1 from residual powders 20 at the end of
the forming. In particular, powders are used which are obtained by
means of gas atomization processes, that is processes capable of
forming granules that are substantially spherical in shape.
[0031] With regard to device 14, the latter is actuated (in a
manner not shown) to translate along a horizontal direction HR
above a surface 21 which defines portion 17 at the top and the
surrounding residual powders 20. At the same time, device 14 is
controlled so as to distribute a powder layer 22 on surface 21.
[0032] Before the passage of device 14 and therefore the depositing
of the powder, surface 21 is arranged at a fixed reference height
(line Q) with respect to the height position of device 14, by means
of adjusting the base plate 13 in height.
[0033] As shown in FIG. 5, device 14 comprises a dispenser 24, for
example an auger dispenser, which is fed with powder from a tank 25
and is controlled so as to cause a quantity of powder to drop onto
surface 21 through a horizontal slit 26 which is made on a bottom
wall 27 of device 14 and is elongated orthogonally to direction HR.
Preferably, dispenser 24 is of the adjustable type for varying the
quantity of powder caused to drop. Furthermore, in the particular
example shown, at least a part of tank 25 constitutes part of
device 14.
[0034] Preferably, device 14 comprises at least one leveling
element, for example a blade 28, which extends parallel to slit 26
and protrudes downwards with respect to the bottom wall 27 so as to
pass on the powder which is dropped through slit 26 in order to
distribute and level such a powder. In other words, with the
passage of blade 28, layer 22 takes on a substantially even
thickness (which was intentionally exaggerated in figures from 1 to
4 for reasons of clarity).
[0035] According to a variant not shown, blade 28 and dispenser 24
constitute part of two members which are separate and which are
actuated separately from one another to move above surface 21.
[0036] On the other hand, in the example shown, blade 28 and
dispenser 24 are fixed with respect to one another. In particular,
device 14 comprises two blades 28, which are arranged on opposite
sides of slit 26, considering direction HR.
[0037] The powders of each layer 22 are subjected to a pre-heating
step to avoid, or at least reduce, the occurrence of deformations
and/or residual tensions of component 1. The temperature of the
powders obtained by means of the pre-heating step is in any case
less than the melting temperature of the material (in the case of
titanium alloy, the pre-heating temperature is for example around
800.degree. C.).
[0038] The pre-heating is carried out by means of a heat source 30
which is movable so as to carry out a scanning on the powder layer
22. In other words, the heat source 30 advances horizontally and
progressively on the powder layer 22 by following the path of
device 14 along direction HR. According to the present invention,
at least for the initial part of the path carried out by the heat
source 30, the latter is moved on the powder layer 22 at the same
time as device 14, so as to reduce the times of all cycles of the
process.
[0039] In the preferred embodiment shown in FIG. 5, the heat source
30 is fixed with respect to dispenser 24 and/or with respect to
blade 28, so as to be part of device 14. In particular, the heat
source 30 has an elongated shape in direction parallel to slit 26
and to blade 28 and is arranged downstream of blade 28, considering
the advancement direction of device 14 along direction HR.
[0040] Preferably, the heat source 30 is of the inductive type, but
generally the tracking of device 14 may also be carried out with
different heat sources (energy beam, electric resistors, etc.).
[0041] With the configuration shown, where a single heat source 30
is provided, the latter defines a back portion of device 14. In
this case, device 14 must be rotated by 180.degree. before
depositing a new powder layer 22, so as to have the heat source 30
always arranged at the tail, considering the advancement direction
of device 14 along direction HR.
[0042] To avoid this rotation about the vertical axis, as an
alternative (not shown) device 14 may comprise two heat sources 30,
arranged at the front and at the back end, respectively, that is
arranged outside with respect to the two blades 28 shown in the
embodiment in FIG. 5. Or, device 14 may carry out the depositing
step while travelling the horizontal direction HR in a single
direction and then be quickly retracted to the beginning of the
path to carry out the next depositing step.
[0043] As a further, albeit less advantageous, alternative, the
heat source 30 may be separate from and be moved separately from
dispenser 24 and from blade 28 above surface 21.
[0044] According to an advantageous aspect of the present
invention, the heat source 30 comprises a plurality of induction
coils 31, which are wound about respective vertical axes 32 and are
arranged in positions distributed, for example along at least one
row, so as to cover a dimension which is at least equal to the
length of slit 26 and/or of blade 28 (that is at least equal to the
width of the powder layer 22), orthogonally to direction HR.
[0045] As shown in FIG. 6, the heat source 30 preferably comprises
two rows 31a, 31b of coils, where each coil of row 31a is coupled
and adjacent to a coil of row 31b, so as to close the magnetic
field lines in such a pair of coils.
[0046] Again, with reference to FIG. 5, the heat source 30
preferably comprises an adjustment device 35 (diagrammatically
shown), which transfers the electric energy to the coils 31
starting from a power supply (not shown) and is controlled so as to
adjust the electrical power fed to the different coils 31, to vary
the average pre-heating temperature of the powder layer 22 and/or
to differentiate the power between the various coils 31 and
therefore vary the temperature between the various areas of layer
22.
[0047] The temperature of the powders during the pre-heating is
preferably kept under control, for example by using a suitably
calibrated infrared sensor. According to the temperature detected,
it is possible to adjust the power of the coils in closed loop, for
example similarly to what provided in common electromagnetic
induction ovens or microwave ovens.
[0048] Machine 11 also preferably comprises an adjustment device
(not shown) for varying the frequency of the electric current fed
to the coils 31. The physical features of the materials treated
(such as the magnetic permeability) and the depth of the powder
layer 22 that must be heated, determine the most suitable choice
for the frequency value.
[0049] Advantageously, device 14 comprises a shield 37, for example
of type similar to the ones used in common cathode ray tubes, so as
to avoid any interferences generated by the magnetic field of the
coils 31 on the other equipment of device 14 and of machine 11.
Shield 37 surrounds the coils 31 and preferably also device 35, on
all sides except for the bottom one, which must be crossed by the
magnetic field lines so as to heat the powder layer 22 by
induction.
[0050] Advantageously, the melting is also carried out for at least
part of each cycle at the same time as the distribution of the
powders and as pre-heating. In other words, the energy beam of
emitter 15 is moved on the powder layer 22 at the same time as
device 14, so as to track the movement of the heat source 30 along
direction HR and therefore further reduce the times of all
cycles.
[0051] As disclosed above, considering FIG. 3, the melting is
carried out in localized areas selected by the control unit 16 on
the basis of the three-dimensional model stored so as to form a new
section 170 above portion 17. During the melting of the powders,
the cross section 170 is "amalgamated" with portion 17 below so as
to form a new portion 170' (shown in FIG. 4). The thickness of
section 170 that was just formed is essentially a function of the
thickness of the powder layer that was deposited by device 14.
[0052] After the melting step, plate 13 is lowered by a
predetermined height (arrow V) corresponding substantially to the
thickness of section 170 that was just formed, so as to bring the
top surface of portion 170' and of the surrounding powders back to
the fixed reference height (line Q).
[0053] At this point, device 14 starts again in the opposite
direction, if necessary after having been rotated by 180.degree.
about a vertical axis, to bring the heat source 30 behind blade 28,
so as to then deposit a new layer of powders (indicated by numeral
23) which are pre-heated and subjected to localized melting in
rapid succession. The process continues this way with the
repetition of the steps of depositing, pre-heating, melting and
lowering the base plate 13, until the three-dimensional model
stored in the control unit 16 is completed, that is until missing
portion 19 is completed.
[0054] At the end of the forming, component 1 is advantageously
cooled by means of a flow of inert gas (for example helium or
argon) introduced into chamber 12, before being detached from the
base plate 13. Other processing steps may be possibly carried out,
for example for completely removing the remaining residual powders
in the cavities of component 1 or for eliminating any traces of the
supports 18.
[0055] The advantages of the above-described manufacturing process
are apparent from what mentioned above.
[0056] Firstly, the fact of moving the heat source 30 above surface
21 together with dispenser 24 and/or with blade 28 allows a
significant reduction of the manufacturing times to be guaranteed
with respect to known solutions in which the pre-heating step is
carried out after having completed the depositing step.
[0057] Moreover, the fact of integrating the heat source 30 in
device 14 allows the volumes to be reduced to the maximum extent
possible and the times between the depositing and pre-heating steps
to be reduced. Furthermore, this way a single movement system (not
shown) is used for moving dispenser 24, blade 28 and the heat
source 30 together above surface 21 along direction HR.
[0058] By using one induction heat source which may operate in
controlled and inert atmosphere for the pre-heating step, it is
possible to avoid the use of electron beams and therefore it is
also possible to process alloys suffering from vacuum
evaporation.
[0059] In particular, device 14 allows the heating efficiency to be
optimized and the volumes to be limited with respect to known
solutions in which induction coils are arranged in fixed
positions.
[0060] Furthermore, the process is extremely flexible, because by
adjusting the power supplied to the various coils 31, it is
possible to fine tune the pre-heating temperature between the
various areas of the powder layer 22 and therefore to optimize the
heating efficiency.
[0061] Finally, it is clear that modifications and variants may be
made to the above-described process and device 14 which are
disclosed with reference to the accompanying figures, without
departing from the scope of the present invention.
[0062] In particular, direction HR might not be rectilinear, and/or
the shape and configuration of device 14 could be different from
the ones shown diagrammatically in the accompanying figures; and/or
tank 25 could be arranged in remote position and connected to
dispenser 24 by means of a conveying tube.
* * * * *